Portable electronic devices such as mp3 players, cameras, and cell phones are typically fitted with a USB port, which allows them to transfer data to or from other controllers or hosts. Using these USB ports, portable devices may conveniently draw current from personal computers to charge their batteries. In light of this convenience, engineers have developed standalone or dedicated USB chargers that expose a USB standard receptacle to the portable devices, allowing them to use the same USB port to charge either from a computer or a dedicated USB charger.
The advent of dedicated USB chargers has, however, increased charging complexity. Now, different type of USB charging ports are available, such as standard USB ports, charging downstream ports, and dedicated charging ports. Moreover, these ports allow portable devices to draw current in different ranges. Portable devices, therefore, have to identify the port type before they can begin drawing current from the ports. Ascertaining the type of port can often become difficult.
To overcome this difficulty, the USB Battery Charging Working Group has introduced a Battery Charging Specification (BCS), which describes a charging port detection handshake protocol, allowing BCS compatible devices to detect the type of USB port before drawing current. Though this protocol allows compatible devices to begin charging, this handshake introduces a problem for legacy devices such as RIM® and Apple® products.
Legacy products do not follow the BCS protocol; therefore, when these devices are connected to a personal computer or USB charger, they may not be able to detect the port type. Moreover, because legacy devices cannot identify the port type, they may be allowed to draw minimal current (80-100 mA) from the charging port or no current at all.
Also, though the BCS indicates the necessary actions for a BCS compliant charging device to perform, it makes no qualifications on the timing of these actions. Some portable devices may require action in a specific timeframe. If the charging device does not respond within this timeframe, the portable device may not be able to draw charging current from the device.
Therefore, there remains a long-felt but unresolved need for a system or method for detecting port type for all types of portable devices including BCS compatible and legacy devices.